The present invention relates to a self-leveling street sewer which, while serving both to collect surface water and to channel such water via a connecting conduit to the main storm sewer, supports a grating over which vehicular traffic can travel. In contrast both to the conventional street sewer and to the various concepts that have already formed the subject matter of previous inventions, the proposed self-leveling sewer does not require the installation of an immobile concrete structure since the frame is supported by the street foundation itself, while the tubular section is coupled to the connecting conduit.
A conventional sewer comprises a concrete structure that consists of a base upon which are seated a plurality of elevating rings up to a predetermined height. The base, which is situated below the frost line, sits upon a cushion of granular material that has been tightly packed in order to prevent the base from shifting over the years and moving the structure away from its predetermined height level. A connecting conduit connects the base to the main storm sewer. A frame, of circular or rectangular shape, as well as a grating of cast iron, are installed upon the upper portion of the immobile concrete structure. This type of installation permanently fixes the level at which the frame sits. The street foundation, which comprises granular material, and layers of paving material, are compacted all about the frame. This rather conventional method of installation, however, is attended by a number of disadvantages. With respect to the pavement, two problems ensue. Firstly, over the years, the foundation of the street settles considerably, a phenomenon that causes the level of the roadway to drop. Since the concrete structure is fixed in place, the frame is incapable of following the downward movement of the roadway surface and accordingly remains at a higher level. Secondly, the freezing that takes place every winter expands the foundation of the street and thereby raises the road surface. Since the depth at which the immobile concrete structure sits renders it insusceptible to such frost action, the frame always remains at its original level and therefore ends up sitting below the roadway surface. Such annual up-and-down movement of the earth (frost in the wintertime and thawing in the spring) gives rise to considerable deterioration in the immediate area of the conventional street sewer.
The underlying immobile supporting concrete structure is also a source of problems for the surrounding street foundation due to the presence of elevating rings that are raised up when the ground freezes. Such elevation of the rings creates a space in which small rocks, which come from the surrounding earth, can become lodged and so act to prevent the elevating rings from returning to their initial position during times of thaw. This opening in the underlying concrete structure permits infiltration of sand and gravel which results in the formation of a cavity in the street foundation and a weakening of the road surface in the immediate vicinity of the street sewer in question. Under loading, such small rocks act like punches to crack the elevating rings and so accelerate the deterioration of the underlying immobile concrete structure. In addition, municipal snow removal equipment may incur damage (when snow plows and graders strike the exposed frames), travellers in vehicles may experience discomfort and private motor vehicles may sustain damage. Frames sitting lower than the roadway surface can, particularly when traveled over by heavy vehicles such as buses, also give rise to vibrations that disturb the quiet in adjacent residential areas.
A number of prior art patents have proposed a variety of concepts in response to the foregoing problems. Canadian patents No. 2, 151, 069 (U.S. Pat. No. 5,470,172) and No.1,287,247 (U.S. Pat. No. 4,906,128) as well as U.S. Pat. No. 3,858,998 feature frames that always sit upon an underlying fixed load-absorbing concrete structure. Furthermore, the frame used in these systems must be adjusted manually.
Canadian patents No.1,270,138 and No.1,172,050 feature a peripheral strip supported upon a base that itself sits directly upon an underlying immobile concrete structure. The frame lifts up during the cold season when the ground expands and returns to its initial level during thaw. In this case as well, the prior art system uses both an underlying immobile load-absorbing concrete structure and a frame that will sit higher than the roadway surface when the street foundation settles some years later.
Canadian patents No. 2,222,954 and No. 2,212,401 (U.S. Pat. No. 6,109,824) feature a frame that is embedded in the street foundation and a section or head that allows the frame to move both vertically and angularly. These parts are designed to adapt to an underlying immobile concrete structure. However, in many cases, such parts cannot always be used to replace conventional street sewers that have already been in use for many years. The aforementioned problems are the most clearly evident in these systems, since it has been noted with respect to many such sewers that the height available between the top of the base and the road surface is not sufficient either to accommodate both parts and frame or to afford enough space to permit their effective operation. This situation has also been noted with respect to a great many conventional street sewers in more recent housing projects where the minimal depth has permitted the use of fewer elevating rings. It is absolutely essential to the proper functioning of the aforementioned inventions that the frame never touch the section or the head, lest it lose its ability to descend again. In addition, the available height must not be too restrictive, since the frame will end up being supported only on top of the ground above the base instead of on top of the street foundation. Since the magnitude of the expansion of the earth through freezing depends on thickness, the earth situated between the top of the base and the frame will add a vertical differential less than the relatively greater thickness of the street foundation that is situated beneath the pavement. In order to increase the space available between the base and the surface of the roadway, it is necessary to lower the base, which greatly increases installation costs. In addition, the presence of rock must be taken into consideration. Furthermore, adequate slope must be maintained for the connecting conduit, which translates into added excavation, and therefore extra costs.
It has been noted with respect to U.S. Pat. No. 2,212,401 (U.S. Pat. No. 6,109,824), that there is a problem of access to the bell that is situated in the base 6 of nearly all street sewers and whose function is to prevent floating debris from entering the main storm sewer and being carried into waterways. In essence, the positioning of the drainage conduit 9 permits maintenance crews to have direct access to said bell, but the notable feature of this invention, which is the eccentric position of the opening in head 5, does not in any way address the issue of access but rather only facilitates the positioning of frame 3 relative to the sidewalk or the curb line. This invention is also attended by problems arising from the lack of similarity between walls 37 and 38, a consequence of which being that both sides of frame 3 cannot sit equally upon the underlying ground, a situation that will likely cause frame 3 to rock back and forth.
In accordance with the novel concept proposed in the present invention, the frame comprises a horizontal or sloping external wall that permits loads to be transmitted directly to the underlying ground. This having been done, the frame compacts the surrounding underlying earth, thus providing for its own support, whereby the frame “floats”, similarly to the pavement, on top of the street foundation. The frame will then perforce, simply, automatically and naturally, and without human intervention, follow, in the manner of the pavement, the up-and-down movements of the street foundation. The simultaneous movements of both frame and pavement will obviate any deterioration of the pavement surrounding the novel structure.
In all prior patents, the immobile underlying concrete structure is needed to support a number of elements that are germane and essential to the invention. Since the novel concept presently proposed does not contemplate any parts requiring support, the underlying fixed concrete structure is not needed. The concrete structure is replaced by a tubular section that is freely connected to the frame at its upper extremity and is coupled to the connecting conduit at its other extremity or, if a tank is present, at a certain distance along the wall thereof. The flexibility of the tubular section permits angular displacements of the frame. A tubular section of greater rigidity is permitted to displace angularly owing to the inclination of the lower wall of the frame. Insertion of a rubber collar between the upper extremity of the tubular section and the lower portion of the frame prevents infiltrations. The frame is free to displace along the tubular section.
This arrangement saves on labour and costs and reduces project complexity. There is no longer any heavy concrete structure to be manipulated, the cost of the tubular section is less than that of the immobile concrete structure and, since there is no frame to damage the compacting equipment and the diameter of the tubular section is smaller, the work of compacting about the tubular section is both facilitated and rendered more effective. Since the available height between the roadway and the connecting conduit may be severely limited, this novel concept can be used for old sewer installations where the connecting conduit is not situated at any great depth. In such cases, it is only a matter of adjusting the tubular section. Where older street sewers are to be renovated, and everything depends on dimensions and depth, the old base can be left in place and the tank of the tubular section slid toward it, or the extremity of the tubular section not having a tank can be connected to the existing connecting conduit, thus further facilitating installation and reducing costs. The space remaining in the base can then be filled in with granular material, which is then compacted.